Aldehydes and alcohols containing one more carbon atom than a starting olefin can be prepared by transition metal-catalyzed reactions of the alkene with carbon monoxide and hydrogen. This reaction is known as hydroformylation or oxo reaction. Aldol condensation of aldehydes is a well-known reaction employed for many years in the production of several commercially important materials in addition to 2-ethylhexanol, for example, the formation of isophorone and mesitylene oxide from acetone. The reaction is not merely base catalyzed, but usually needs a strong base catalyst in order to proceed satisfactorily. Often the strong bases used as catalysts in aldol condensation are alkali metal hydroxides, especially under aqueous or partly aqueous conditions. Hence, it is well known that hydroformylation and aldol condensation are carried out as two separate processes.
Worldwide production and consumption of hydroformylation products (or oxo chemicals) exceeds 8.8 million metric tons per year. The applications of oxo products are in the manufacture of soaps, detergents and plastisizers. The largest share of almost 40% of total production capacity is covered by 2-ethylhexanol. Over 90% of world consumption of normal-butanal, which is synthesized from Cn-alkene where n is 3, is in a hydroformylation reaction where it is converted to 2-ethylhexanol and n-butanol while all detergent and C6-C13 plasticizer oxo aldehydes are converted to their corresponding alcohols. 2-Ethylhexanol, a valuable intermediate product for the chemical industry, is being used in the production of dioctyl phthalate, other plasticizers, coatings, adhesives and specialty chemicals. In these end use areas, it contributes significantly to many high performance characteristics such as flexibility, good adhesion, lower emissions and fuel performance improvement. Additionally, 2-ethylhexanol is oxidised to 2-ethylhexanol acid. This acid can also be manufactured by oxidation of 2-ethylhexanal produced by selective hydrogenation of 2-ethythexenal. 2-Ethylhexanoic acid is used for modifying alkyd resins while 2-ethylhexanal can also be used as a raw material for perfumes.
Commercially, butanal (both normal and iso) are initially produced by reaction of Cn-alkene, where n is 3, carbon monoxide and hydrogen namely hydroformylation or oxo reaction using organophosphine metal complex as a catalyst. Normal-butanal is separated from the product mixture by distillation process. The normal-butanal thus obtained from distillation process is subjected to condensation reaction namely aldol condensation reaction in presence of aqueous base lie KOH and NaOH etc. to give 2-ethylhexanal. The aldol condensation product, 2-ethylhexanal, is further subjected to hydrogenation reaction to get 2-ethylhexanol with use of appropriate catalytic of Nickel or Copper. The multi-steps involved in the production of 2-ethylhexanol from Cn-alkene, where n is 3, via hydroformylation, aldolization and hydrogenation is shown below:

It has been estimated for the production of 2-ethylhexanol that approximately 25-30% of its selling price involves the cost of the product purification, recovery and waste treatment. The high capital expenses are also connected with the handling of strong liquid bases like KOH and/or NaOH during aldol condensation reaction. In addition to that, presently, about 1-1.5 tons of spent catalyst is being generated for every 10 tones production of 2-ethylhexanol. The industrial manufacture of 2-ethylhexanol involves very high capital cost since the synthetic strategy for production of 2-ethylhexanol (Scheme 1) has many drawbacks as written as (i) the synthetic strategy of 2-ethylhexanol from Cn-alkene, where n is 3, is a three step process is not economical from industrial and energy perspective. (ii) the use of hazardous reagents liquid KOH or NaOH in stoichiometric amount for aldol condensation in the second step and effluent problem in disposal of hazardous KOH(NaOH which is not eco-friendly route. (iii) the handling of liquid base KOH/NaOH and post synthesis work-up in separation of spent KOH or NaOH from reactants increases the capital cost of 2-ethylhexanol.
It is, therefore, highly desirable, to develop an eco-friendly multi-functional catalyst, which can reduce the multi-steps involved for the production of C2(n+1), saturated and unsaturated aldol-derivatives form C subs. n-alkenes, more specifically, production of 2-ethylhex-2-enal and/or 2-ethylhexanal and/or 2-ethylhexanol from Cn-alkene, where n is 3, in a single step. Many efforts are being carried out to accomplish the goal, some of them discussed in background of invention.
Reference is made to O. R. Hughes et al. U.S. Pat. No. 3,821,311 titled “Production of aldehyde from olefins” which describes a process related to production of aldehydes. More particularly this patent relates to production of C2(n+1) saturated and unsaturated aldehyde from Cn terminal olefins. The main drawback is the use of hazardous aqueous base KOH for aldolization of aldehydes. The selectivity of C2(n+1) saturated and unsaturated aldehyde from Cn terminal olefins is not more than 23%.
C. R. Greene et al. in U.S. Pat. No. 3,278,612 titled “Oxo process using cobalt carbonyl and tertiary phosphine under basic conditions” disclose a process for production of alcohols from organic compounds having less number of carbon atoms in the chain. More particularly the patent relates to production of Cn+1 and C2(n+1) alcohols from Cn olefins such as butanol and 2-ethylhexanol simultaneously from Cn-alkene, where n is 3. The patent discloses catalytic synthesis of alcohols in presence of certain complex hydroformylation/hydrogenation catalysts in a particular reaction medium. The main drawback is the use of cobalt catalyst system for hydroformylation reaction, which is known to be inferior than rhodium and the use of hazardous amines and KOH for aldolization of aldehydes.
R. Paciello et al. in U.S. Pat. No. 5,689,010 titled “Preparation of higher aldehydes” disclose a process for preparing aldehydes with a higher number of carbon atoms and high selection by reacting olefins, in particular from petrochemical refinery products, by a hydroformylation with aldol condensation using a mixed catalyst of rhodium-carbonyl-phosphines and Mannich catalyst. The main drawback is use of Mannich catalyst for aldolization of aldehydes, since the catalyst is not eco-friendly.
J. F. Knifton et al in U.S. Pat. No. 4,469,895 titled “Process for preparing alcohols from olefins and synthesis gas” disclose an improved process of preparing predominantly linear alcohols by the steps of contacting a mixture of terminal and/or internal olefins and synthesis gas with a catalyst system comprising a ruthenium-containing compound in conjunction with one or more tertiary amine promoters, dispersed in a low melting quaternary phosphonium salt and heating said resultant reaction mixture under a pressure of 7 kg/cm2 or greater at a temperature of at least 50° C. for a sufficient time to produce alcohols. The main drawback is that this process produces aldehyde and/or alcohols of Cn+1 carbon atom from Cn olefins not aldehyde and/or alcohol of aldol derivatives C2(n+1) from olefins Cn in hydroformylation conditions in single step. Moreover, the hydrogenation of aldehyde products to corresponding alcohols is a common feature under hydroformylation conditions.
J. S. Yoo in U.S. Pat. No. 3,991,119 titled “Hydroformylation over cobalt on support comprising separate alumina phase” discloses a new, solid catalyst suitable for the hydroformylation of low molecular weight olefins. The catalyst composition is a hydrido-cobalt or nickel carbonyl-Group VA electron donor ligand complex on a solid, acidic, silica-based support. Preferred electron donor ligands are phosphines and tertiary amines. A preferred catalyst support contains amorphous silica-alumina and alumina. The main drawback is the maximum Gas Chromatography (GC) % of 2-ethylhexanal obtained was less than 10% from Cn-alkene, where n is 3. Additionally, cobalt metal catalyst system that is inferior to rhodium metal system is used and the reaction condition and products yield are inferior. The solvent system is benzene, which is known to be a carcinogen. The catalyst system has not been used for other alkenes except Cn-alkene, where n is 3.
W. Bueschken et al. in U.S. Pat. No. 5,756,856 titled “Process for the preparation of 2-ethylhexanal” describes a process for the preparation of 2-ethylhexanal by catalytic hydrogenation of 2-ethylhex-2-enal, wherein the hydrogenation is carried out in a plurality of two or more series-connected loops, wherein each loop involves the use of one reactor, which comprises: (a) feeding 2-ethylhex-2-enal and hydrogen to an upper part of a reactor to catalytically hydrogenate said 2-ethylhex-2-enal to produce a hydrogenation product, (b) recycling a portion of said hydrogenation product back into said upper part of said reactor, (c) feeding the remainder of said hydrogenation product from said reactor to an upper part of a subsequent reactor wherein 2-ethylhex-2-enal is catalytically hydrogenated to produce a subsequent hydrogenation product, and wherein a portion of said subsequent hydrogenation product has been recycled and is fed with said remainder of said hydrogenation product to said upper part of said subsequent reactor, (d) repeating step (c) until the subsequent reactor is the last reactor, (e) recovering the remainder of said subsequent hydrogenation product from said last reactor, and (f) obtaining 2-ethythexenal from the product of step (e). The main drawback is 2-ethylhexanal is produced by catalytic hydrogenation of 2-ethylhex-2-enal and not from Cn-alkene, where n is 3, in single step.